Electric safety device



(No Model.) 2 SheetsSheet 1.

E. THOMSON. ELEGTRIG SAFETY DEVICE. No. 550,733. Patented Dec. 3, 1895.

/NV NT OH fad/22W A TTOHNE Y8 N. DC. ANDREW BYGRANAM.PHOTULITHQWASMNGTO (No Model.) 2 Sheets-Sheet 2,

E. THOMSON. ELECTRIC SAFETY DEVICE.

Patented Dec. 3,1895.

h /aw ATTORNEYS ANDREW B.GRAHAM PHOTOUTNQWASHINGTONJ C UNITED STATES PATENT OFFICE.

ELIIIU THOMSON, OF LYNN, MASSACHUSETTS, ASSIGNOR TO THE THOMSON- IIOUSTO). ELECTRIC COMPANY, OF CONNECTICUT.

ELECTRIC SAFETY DEVICE.

SPECIFICATION forming part of Letters Patent No. 550,733, dated December 3, 1895. Application filed May 19, 1887. Serial No. 238,731. (No model.)

To all whom it may concern.-

Be it known that L-ELIHU THOMSON, a citizen of the United States, and a resident of Lynn, in the county of Essex and State of Massachusetts, have invented a certain new and useful Electric Safety Device, of which the following is a specification.

The object of my invention is to provide a simple and efficient lightning arrester or IO safety device for application to two main electric conductors between which a considerable difference of potential exists.

My invention is designed especially for application to those cases where the two mains I 5 form, respectively, the positive and negative mains of a system in which the translating devices are supplied in multiple are and in which the mains carry currents of considerable potential. The translating devices fed from the mains may be electric motors, i11- candescent lamps in series multiple or induction-coil primaries, the secondaries of which latter are of comparatively low potential and are used to feed local lines with incandescent lamps or other devices.

My invention is applicable to cases where either a continuous or an alternating current is employed.

The invention relates, also, to the connec- 0 tion of suitable safety-fuses where the lightning-arrester is applied to branch wires which connect to the translating devices.

My invention relates more particularly, however, to the provision of a safety device 3 5 to insure freedom from short circuits between the mains of a multiple-arc system induced by lightning or atmospheric discharges.

My invention is carried out by the employment of devices acting in a similar way to 0 that described in my Patent No. 321,464.,

dated July 7, 1885, in that I make use of a magnet or equivalent arc-rupturin g device in connection with an arrester.

My present invention, however, consists of a double pole lightningarrester or an arrester for both poles of the circuit combined in asimple compact shape, the design being to guard against atmospheric discharges occurring on one or both branches of a multipleare line, so that such discharges may be carried to earth and to rupture any cross or short circuit forming at the time from one branch of the main to the other. As an additional element of precaution in such a device or attaclnnent, I use long safety-fuses in each wire leading through the lightning-arrester case.

My invention will be understood from the following description.

Figure 1 shows my safety arrangements in elevation in a case or boX B. Fig. 2 shows a vertical cross-section of the same through the center of the box. Fig. 3 shows the essential electrical elements of my invention, separated for clearness. Fig. 4, shows an application of the invention and the connections, Ate. Fig. 5 shows a modified disposition. Fig.

(5 shows still further modifications and dispositions of the parts. Figs. 7, 8, and 9 show modifications in the arrangement of the lightning-arrester elements of my invention.

It is to be understood that wherever I have shown as an arc-rupturing device a magnet or magnet-coil the magnetic field of which is applied to the circuit formed between the two mains and across the arrester in such way as to interrupt the current on such circuit, any equivalent arrangementsuch, for instance, as those described in my prior patent above referred tomay be substituted therefor. It is also to be understood that the fuses which I use in my invention may be, if sufficiently long, used as arc-rupturing devices, this being indicated in Fig. 9.

In Figs. 1 and 2 B B is a box or casing of metal, such as cast-iron, proof against leakage 8 5 of rain to its interior when established out of doors, and preferably provided with lugs L L, by which it may be supported on a wall or post and at a slight distance therefrom. It is provided with a cast-iron cover 0, screwed on 0 or hinged, as preferred. In the open space in its interior is mounted a slab of non-conductor S, such as slate, steatite, or sandstone, which has been thoroughly dried and water-proofed by soaking in warmed paraffine or other suitable material. The mode of attachment of this slab to the interior of the box is of no moment. It may be supported in any way, as by screws or lugs. The slab carries on its face posts 0 (l and G H, to which are connected the main branches M M of line-wires N N, coming from a system of overhead or underground wires, and representing two sides of a multiple are or other circuit with a high-potential difference between the portions of the two wires where the arrester is applied. The wires M M enter through hard-rubber bushings b b, flared and expanded downward so that rain may not enter the box, and connect first to the posts 0 (Z, from which they connect by fuse-wires F F, of lead and tin or other fusible alloy, to the posts G H, as shown. From the latter posts connection is made by i11- sulated wires passing downward through the pipe P to any suitable device, such as a motor or induction coil placed within or without a building. The fuses F F are adapted to melt and open the circuit if the wires in the pipe P or in the device connected thereto both become short-circuited or demand abnormal current.

Attached to or carried by the posts 0 (Z are lightningarrester plates 1 4, opposite each of which is established at a small distance an opposing plate 2 3, connected to earth through the coils of an arc-rupturing magnet at A. The plates 2 3 are each carried, as shown, by feet or brackets running from the slate slab S. These plates 1, 2, 3, and 4 are tapered upward in gothic-arch form and at their lower ends are quite close together-say one-sixteenth of an inch, or thereabouts. The intermediate plates 2 3 are connected to earth by connections carried through the coils of magnets A A to the pipe P, which may be grounded.

On the occurrence of a lightningdischarge which induces or produces an instantaneous flow of high-potential current in either one or both of the mains N N and wires M M, such flow or discharge finds its way to ground by springing across the space between the plates 1 2 or 3 4; but such an action may cause a circuit to exist between N and N by an are forming across the arrester-plates. To understand the actions which occur, reference may be had to Fig. 3. Here l N M M, connected to e (Z, are in connection through the fuses F F with the posts G H, which are in turn connected to the wires 00 y, leading to the local distributing or translating devices.

The plate 1 is carried by the post 0 and plate 4 by (Z, and these plates, together with the intermediate separated plates 2 3, are located between the poles of a magnet A A, so that their separated spaces may be subjected to an intense magnetic field, but preferably at such a distance from the poles that a discharge cannot pass to the poles themselves. A coil on the magnet is connected to each of the pieces 2 3, leading therefrom to earth E. The direction of the winding is such that a current passing from 1 to 2 and through the coil on the leg A, connected therewith, and back through the other coil on the leg A and the plate 3, and across the space between the plates 4 to the plate 4 will be in such direction as to cause magnetism of a definite polarity to be developed in the poles between which the plates are placed, and in accordance with the principles of my patent before referred to. The connections are more definitely seen in Fig. 4, as other parts are left out for clearness. The wires M M are shown as branches from the main N N, and the posts GH lead to the primary R of an induction coil whose secondary S leads to the lights on the local circuit. Now should a short circuit occur in the line leading from G H to R the fuses F F, one or both, will melt and interrupt the connection. A lightning discharge, however, or an induction from a lightning-discharge occurring on the system will find ground from the plates 1 4, (either or both,) to earth connection at E. If such discharge goes by only one path, as from 1 to 2, no particular harm will result, as it will cease at once; but if while the high potential exists such a discharge passes so as to cause a spark to pass between 1 and 2 and also between 3 and 4, there would be a circuit or are formed from N to N through the arrester-plates 1 2, thence through the common connection of 2 and 3 to 3 and 4, and said circuit having been established would be maintained by the current derived from the generating source, which current, passing across the lightning-arrester from one main to the other, would finally destroy the arrester. The magnet-coils A A would,-however, come into circuit and energize the magnet, producing strong poles on each side of the arresterplates. The connections, if made in accordance with my former patent, above referred to, will, however, result in the production of magnetism in such direction as to drive the spark or are between the plates outward and upward to the wider portions of the space between them and finally cause it to rupture, restoring the line to its normal condition. It is sometimes advantageous to reverse the or der of connections through the fuses, as in Fig. 5, by bringing the branch mains M M to the fuses first, after which connection is made to the lightningarrester plates 1 4 and to the leading-wires 00 y. The only difference is that besides the rupturing of a possible short circuit by the magnet acting 011 the are between the plates the fuses themselves may be melted and so increase the distance through which the discharge would have to leap.

It is not essential that the earth connection be placed, as shown Figs. 3 and 4, at the middle of the circuit through the magnet, as it may be placed, as indicated by the dotted lines, at E or E ,it being only essential that the coil A shall be energized by a discharge passing from one side to the other through the spaces 1 to 2, 3 to 4. In this case, however, an artificial resistance is preferably placed in the ground-wires.

It will be seen, also, that an alternating-current discharge will alternate the magnetism of the magnet in such a way as to drive the are upward and outward, and it is not, therefore, different in its effects in such a structure from continuous currents.

Instead of connecting the fuses F F inside the box I) B, Fig. l, and in the way shown in Fig. 5, the fuses themselves or accessory fuses may be connected outside the box, as indicated in Fig. 6 at F, where the main branch M is carried through the fuse F before reach ing the first arresterplate and from there connected to the local line. In this case, however it is advisable to inclose the fuse-wire in an outer casing or tube T, of glass, which is dried and plugged at each end by a tight plug, such as rubber corks K K. It is also advisable in order to prevent leakage of current in case the fuse F is interrupted or melted open and rain or water is falling 011 the ex terior of the tube T to recurve it back on its up per part, as at Z, so as to shed the water from above, maintaining a portion of the space underneath the recurved portion dry. However, if the corks or plugs K K are but loosely placed in position one or the other of them will be driven out by the explosion of the fusewire, thereby violently rupturing the connection and absolutely preventing the passage of current from the wire M to the local wire, even during the heaviest rain. Such an arrangement is shown in Fig. 6, and is a very useful accessory, even when the parts shown in Figs. 1 and 2 are used, and as it provides an additional and complete safeguard against possi ble short circuits of the main wires through the lightning-arrester from leakage, arcing, or atmospheric disruptive discharge.

Fig. 7 simply shows that either of the coils A A may be applied to rupture the are or spark forming between 1 2 3 4i upon the existence of a strong induction from atm osphcric discharges.

In Fig. 8 the two plates 2 3 of Fig. 3 are shown as combined in one plate 23, connected to earth, and the magnet coil or coils of the arrester-magnets for rupturing the are, as at A" A", connected between the post 0 and plate 1. and post (Z and plate 4, so that any discharge passing to earth goes also through the coils A" A, either or both. The directions of winding are, as before, such as will repel an are forming between the arrester-plates to the wider portion of the space between the plates, so as to break it or prevent its continuance.

Sometimes the fuse-wires maybe used as the arc-rupturing device in place of the magnet, when arranged as in Fig. 8. Fig. 9 shows how they may be substituted.

Connected from the post 0 to 1 and from the post d to plate +1 are fine fuse-wires F F of sufficient length to render impossible the corn tinuance of the short-circuiting are across from c to (Z, through the fuses, and in the spaces between the plates 1 2 3 -:L. If such discharge takes place, the fuses F F melt and open a wide space. The disadvantage, however, of this arrangement is that it only acts once to rupture the arc and throws the lightning-arrester practically out of use thereafter. New fuse-wires would have to be sub stituted to put the apparatus into action again. I therefore, while considering this arrangement as a possible one for one dis charge, do not consider it as good an arrangement as the magnetic arc-rupturing device, which is present and ready to work for numerous discharges or short circuits following one another.

Other arc-rupturing devices-such, for instance, as are described and shown in my prior patent-may obviously be used.

What I claim as my invention is- 1. The combination with electric mains supplying devices in multiple, of a lightning arroster for both poles of the circuit, an arc rupturing magnet or magnets for rupturing an are following a discharge over either pole, and means for rupturing a cross or short circuit from one main to the other through the lightning arrester resulting' from a discharge to ground from both mains together.

2. The combination with the double pole lightning arrester connected to the two mains or wires, of an electro magnet whose mag netic poles embrace or act upon the spaces between both sets of arrester plates or poles, and a coil or coils for said magnet in a circuit from one main to the other through the arrester, as and for the purpose described.

3. The combination with two sets of lightnin g arrester plates connected respectively in ground circuits from high potential mains and mounted together upon a suitable base plate of insulating material, and an arc rupturing electro magnet whose poles embrace the spaces between the plates in each ground circuit, said electro magnet having coils in a circuit formed from one main to the other through the arrester plates and across the spaces between them.

l. The combination with two sets of lightning arrester plates or electrodes connected respectively to opposite poles of an electric circuit, of an electro magnet whose poles are applied so as to rupture any are forming across the spaces between said plates and two energizing coils for said electro magnet connected respectively in the two ground circuits from the mains and joined together so that any current passing from one main to the other will energize the magnet by the influence of both coils.

5. The combination with electric mains or wires supplying devices in multiple,of a lightning arrester ground connection from each pole, and fuse wires in the connection between the main and lightning arrester made of such length as to operate to prevent the continuance of a short circuiting are from one main to the other through the wires and the lightning arrester.

6. The combination, substantially as described, with lightning arrester plates tapering upward to form a gradually increasing IIO space as described, and an are rupturing an earth connection from an intermediate magnet adapted to develop magnetism suit point of the coil circuit. able for propelling or forcing; the are toward Signed at Lynn, in the county of Essex and the Wider portion of the spaces between the State of Massachusetts, this 17th dayof May, plates. A. D. 1887.

7 The combination, substantiallyns de- ELHIU ,IFHOMSON scribed, with two mains, of the terminals 1, 4, connected respectively to said mains, the \Vitnesses: terminals 2, 3,1)laced between the first and E. XVILBUR R1012, J12, 1o connectedtogethei-throughmagnet coils, and .T. W. HBBONEV. 

